I think it is just an IE issue since it does the same thing on my Mac.
To get to my
CUPS interface I type localhost plus the port so it looks like this localhost:631. Works just fine in everything except IE. Something about IE that doesn't understand localhost so you have to type the IP of localhost. Of course this is the same for getting to Apache expect for the fact that there is no need to add the port number as it defaults to port 80.